Electrochemical stabilization of soils and other porous media

Abstract

Suitable electrolyte conditioning at the electrodes greatly facilitates the transport of desired ions through soil, enhancing the ability of electrokinetic processes to stabilize the soil through cementing reactions. Cationic species are injected at the anode, and anionic species at the cathode, with suitable electrolyte conditioning. For example, if acid or base formation negatively affects transport, chemical conditioning is used to neutralize the acid or base products of electrolysis. Ionic species can be transported through soil at rates of several centimeters a day, even in soils such as clays having a low hydraulic conductivity. Electroosmotic transport can be minimized by appropriate conditioning of the pore fluid chemistry. For example, placement of chemical conditioners with smaller cations at the anode compartment and larger anions at the cathode compartment, or increasing the ion content of the pore fluid (e.g. by acidification) can help minimize electroosmotic transport and any of its adverse effects on species transport. The cations and anions are preferably selected to form cementatious precipitates in the soil. Thus when cationic species are injected at the anode and anionic species are injected at the cathode, stabilization reactions can prevail in the soil as the result of cross-transport of species, and a homogenous and uniform cementation and stabilization can be achieved in a short time.

We claim: 
     
       1. A process for strengthening a soil by the addition of a cementing agent comprising an anion and a cation, wherein the combination of the anion and cation in the soil forms a cementitious product, wherein said process comprises the steps of: (a) applying an electric field in the soil between an anode and a cathode;   (b) supplying water to the soil near the anode;   (c) introducing the cation to the soil near the anode, whereby the cation migrates through the soil in the direction from the anode towards the cathode;   (d) introducing the anion to the soil near the cathode, whereby the anion migrates through the soil in the direction from the cathode towards the anode; and   (e) either introducing a base to the soil near the anode to neutralize protons generated by electrolysis of water at the anode; or introducing an acid to the soil near the cathode to neutralize hydroxide generated by electrolysis of water at the cathode; or both; whereby the cation and the anion are dispersed through the soil between the anode and the cathode, and whereby the combination of the anion and cation in the soil forms a cementitious product.     
     
     
       2. A process as recited in claim 1, additionally comprising the step of supplying water to the soil near the cathode. 
     
     
       3. A process as recited in claim 1, wherein the cation comprises H + , Ca ++ , Mg ++ , Fe ++ , Fe +3 , Al +3 , or NH 4   + . 
     
     
       4. A process as recited in claim 1, wherein the anion comprises OH - , SO 4   -2 , PO 4   -3 , CO 3   -2 , SiO 3   -2 , SiF 6   -2 . 
     
     
       5. A process as recited in claim 1, wherein said steps of introducing the cation and introducing the anion are performed simultaneously. 
     
     
       6. A process as recited in claim 1, wherein said steps of introducing the cation and introducing the anion are performed on an alternating basis. 
     
     
       7. A process as recited in claim 1, wherein the cation comprises Ca ++ , and wherein the anion comprises SO 4   -2 . 
     
     
       8. A process as recited in claim 1, wherein the cation comprises an oxyanion containing aluminum, an alkali metal cation, an alkaline earth cation, or an alkyl ammonium cation. 
     
     
       9. A process as recited in claim 1, wherein the anion comprises an oxyanion containing sulfur, an oxyanion containing phosphorous, an oxyanion containing silicon, a fluoroanion containing sulfur, a fluoroanion containing phosphorous, or a fluoroanion containing silicon.